Project Summary While less frequent than hepatocellular carcinomas (HCC), intrahepatic carcinomas (ICC) are a lethal condition with rising incidence rate and, currently, few treatment options. We recently demonstrate that fatty acid synthase (FASN) activity is required for efficient growth of HCC but not for ICC. Given the essential role of fatty acids for membrane synthesis, signaling molecules, and energy substrates this led us to hypothesize that ICC relies on the uptake of exogenous free fatty acids (FFA). Importantly, cell surface molecules have been identified that that are required for efficient uptake of free fatty acids from the circulation. As these molecules have already been shown to be drugable targets, in principle, they might offer new treatment approaches for this deadly disease. Our central hypothesis that protein mediated fatty acid uptake is required for ICC growth in vivo to generate as yet unknown signals that cannot be provided via de novo synthesis of fatty acids. This hypothesis is supported by key preliminary data showing that ICC, but not HCC, express the classical hepatic fatty acid transporters Slc27a2 and Slc27a5 and that ICC isolated primary tumor cells display a robust uptake of exogenous fatty acids. Moreover, using novel assay to determine changes in fatty acid uptake during tumor growth in vivo, we were able to show higher exogenous long-chain fatty acid uptake by ICC tumors compared to an HCC model. Importantly, loss of Slc27a5 diminishes ICC growth in experimental tumor models in spite of FASN expression. Preliminary lipidomics studies comparing lipid compositions in normal and end-stage ICC and HCC models showed significantly higher fatty acid levels in ICC tumor laden livers compared to HCC and for some lipid species even surpassing concentrations found in normal liver. These studies also have begun to shed light on the metabolic fate of the exogenous fatty acids, which might lead to identification of key signals uniquely provided by exogenous fatty acids. Here, using mouse model systems and human ICC PDX, we will determine when and to what extend exogenous FFA uptake is required for the growth of ICC, how it is facilitated, and what unique roles Slc27 driven FFA uptake provides.